What eight minutes of OBD-II data reveal about a cold engine

Why record the whole drive?

A scan tool can tell you the coolant temperature at the instant you check it. But it cannot reconstruct how quickly the engine warmed up unless those earlier readings were saved. In this session, the sequence itself is the useful information: an initially cold engine, a rapid temperature rise, and a short period of relative temperature stability.

1. The warm-up curve

Figure 1. Every coolant-temperature reading in the supplied CSV, plotted against elapsed time. Points are connected to make the trend easier to see; the intervals between samples are not continuous measurements.

The first recorded coolant temperature was 11°C (52°F). After approximately three minutes it reached 54°C (129°F). At 5 minutes 44 seconds, it reached a recorded peak of 85°C (185°F). Subsequent samples remained between 82°C and 84°C through the end of the session.

2. The engine was operating, not just idling

Figure 2. RPM samples, recorded at their own timestamps. The maximum recorded RPM was 2,721.

Figure 3. Speed readings from the export. The CSV does not state the speed unit, so values are deliberately shown in export units rather than assuming mph or km/h.

The engine's RPM varied substantially, with readings as high as 2,721 RPM. Speed readings reached 42 in the export's unspecified units. The temperature curve therefore reflects warm-up during actual vehicle operation rather than a controlled stationary idle test.

Because the adapter polls parameters sequentially, RPM, speed, and coolant samples do not necessarily share identical timestamps. These graphs show trends; they should not be interpreted as millisecond-level correlations.

3. Other signals recorded

The same session contains engine load, manifold absolute pressure (MAP), throttle position, ignition timing advance, short-term fuel trim (STFT), long-term fuel trim (LTFT), and two intake-air temperature samples. Those measurements may help explain specific operating events in a longer comparative study.

For example, the recorded STFT values ranged from −18.8% to +7.0%. Fuel trims naturally change with operating conditions and control mode. Without additional context, these values alone do not justify diagnosing a rich-running condition or another fault.

4. What one snapshot would miss

Suppose we had connected a scanner only near the end of this drive. It would have shown coolant around 82–84°C. That would tell us the engine was warm, but not that it began at 11°C, reached 54°C at about three minutes, and peaked at 85°C less than six minutes after recording began.

The value of continuous car data is not merely collecting more numbers. It is preserving the sequence so that changes, timing, and relationships can be examined later.

How this recording was made

The owner reported that the S10 had been parked overnight. Recording was initiated after the ignition key was turned on and just before the engine was started. However, the first RPM value actually present in the CSV is 1,083 RPM, so the exported data does not capture the starter-cranking interval or establish the exact instant of ignition. The first coolant and RPM readings are both timestamped 16:29:00.

The export covers 16:29:00–16:37:15 on October 17, 2026, containing 276 rows across ten metrics. Measurements were taken at different times as parameters were polled. This is one vehicle and one drive, not a controlled comparison or proof of a particular mechanical condition.

Technical note: This case study reports the supplied measurements as recorded. It is educational information, not a substitute for a mechanical inspection. Original session identifier: 1F8A1008-4682-4972-8F98-40711314DA87.